In Release (R) 8/9 of a Long Term Evolution (LTE) system, a Common Reference Signal (CRS) is designed in order to measure the quality of a channel and demodulate a received data symbol. A User Equipment (UE) may measure the channel through the CRS so that the UE is supported to perform cell reselection and to switch to a target cell and the quality of a channel is measured when the UE is in a connected state. A connection may be disconnected by a physical layer via a high layer-related wireless link connection failure signaling at a relative higher interference level. In LTE R10, in order to further improve the average spectrum utilization of cells, the spectrum utilization of cell edges and the throughput of each UE, two types of reference signals are defined respectively: a Channel State Information-Reference Signals (CSI-RS) and a Demodulation Reference Signals (DMRS), wherein the CSI-RS is applied to channel measurement, a Precoding Matrix Indicator (PMI), a Channel Quality Indicator (CQI) and a Rank Indicator (RI) need to be fed back by an UE to an Evolved Node B (eNB) may be calculated by the measurement to the CSI-RS, The DMRS is applied to demodulation of a Downlink Shared Channel (DSC), and the DMRS demodulation may use a beam scheme to reduce interference between different receiving sides and different cells, reduce performance reduction caused by codebook granularity and reduce the cost of a downlink control signaling to a certain extent.
In LTE R8, R9 and R10, Physical Downlink Control Channels (PDCCH) are mainly distributed in the first 1, 2 or 3 Orthogonal Frequency-Division Multiplexing (OFDM) symbols of a subframe and specific distribution needs to be configured according to different subframe types and the number of CRS ports, as shown in Table 1.
TABLE 1Number of Number of PDCCHPDCCHOFDM symbolsOFDM symbols Subframe(NRBDL > 10)(NRBDL ≦ 10)Subframe 1 and subframe 6 in1, 22subframe type 2a Multicast-Broadcast Single1, 22Frequency Network (MBSFN)subframe on Physical DownlinkShared Channel(PDSCH)-supported carrier, a CRSis configured as 1 port or 2 portsa MBSFN subframe on22PDSCH-supported carrier, a CRS isconfigured as 4 portsa subframe on transmission carrier00not supporting PDSCHa Non-MBSFN subframe (except1, 2, 32, 3subframe 6 of frame structural type2) configured as PositioningReference Signal (PRS)All other conditions1, 2, 32, 3, 4
Each receiving side needs to perform blind detection according to the first 3 symbols, the initial location of blind detection, and the number of elements of a control channel are related to the Radio Network Temporary Identities (RNTI) allocated to receiving sides and different control information. Generally, the control information may be divided into common control information and dedicated control information. The common control information is generally put in a common search space of a PDCCH while the dedicated control information may be put in a common space and a dedicated search space. After blind detection, the receiving side determines whether there is a common system message, downlink scheduling information or uplink scheduling information in a current subframe. Since such downlink control information lacks Hybrid Automatic Repeat Request (HARQ) feedback, a bit error ratio as low as possible needs to be ensured in the detection.
In an LTE R10 heterogeneous network, since different types of base stations have relatively strong interference, in consideration of interference problem to a Pico by a Macro eNB as well as the interference problem to a Macro eNB by a Home eNB, it is put forward that the problem of mutual interference between different types of base stations is solved by a resource muting scheme. A specific resource muting scheme may be divided into a muting scheme based on a subframe, e.g. an Almost Blank Subframe (ABS) scheme, or may further be a resource element-based scheme, e.g. a CRS muting scheme.
However, the schemes above not only increase resource waste, but also greatly limit scheduling, especially when ABS configuration of a Macro eNB is considered. More ABSs will be configured by the Macro eNB if more Picos are distributed, which will greatly influence the Macro eNB to increase scheduling delay while increasing resource waste. In addition, the interference problem of CRS resources and data resources cannot be solved, the interference between the data resources cannot be solved by the muting CRS scheme either. In addition, the schemes above, with bad backward compatibility, may need more standardization efforts while increasing access delay.
More users may be introduced in LTE R11 to perform transmission on a MBSFN subframe, which will result in capacity deficiency of 2 OFDM symbols of a PDCCH which is applied to bearing and configured by a MBSFN. In order to guarantee backward compatibility for R8/R9/R10 users, new resources for transmitting control information need to be explored on PDSCH resources. In addition, a Coordinated Multi-Point Transmission (COMP) technology is introduced in R11. Such technology can solve the interference problem between different types of cells by a space division scheme, save resource cost, avoid resource waste caused by muting, and reduce limitations on scheduling. However, the problem cannot be solved by the space division scheme according to present time domain PDCCH mode. In addition, considering the backward compatibility for R8 and R9, such control channel as a time domain PDCCH must be retained. In this case, how to solve the interference between control channels by space division technology needs to be studied carefully.